▎ 摘　　要

NOVELTY - Constructing a highly-sensitive nitrogen dioxide gas sensor based on a Van der Waals junction film involves preparing semiconductor quantum dots by one-step chemical synthesis without adding any surfactant, carrying out spin-coated uniform modification on semiconductor quantum dots with graphene, and controlling annealing conditions to optimize the Van der Waals contact between the semiconductor quantum dots and graphene. The specific method involves: (1) preparing molybdenum disulfide quantum dots using one-step chemical synthesis by (1a) dissolving sodium molybdate dihydrate in deionized water and ultrasonically dispersing to obtain a solution (A), (1b) dissolving thiourea in ethanol and ultrasonically dispersing to obtain a solution (B), (1c) evenly mixing the solutions (A) and (B), then putting into a reaction kettle, and heating to obtain a suspension and (1d) collecting the suspension in step (3), dispersing in an ice bath, ultrasonically processing and centrifuging. USE - The method is useful for constructing a highly-sensitive nitrogen dioxide gas sensor based on a Van der Waals junction film. ADVANTAGE - The construction method is simple and controllable, and has high repeatability, hence it has obvious application value. The gas sensor exhibits excellent response cycle stability and selectivity. DETAILED DESCRIPTION - Constructing a highly-sensitive nitrogen dioxide gas sensor based on a Van der Waals junction film involves preparing semiconductor quantum dots by one-step chemical synthesis without adding any surfactant, carrying out spin-coated uniform modification on semiconductor quantum dots with graphene, and controlling annealing conditions to optimize the Van der Waals contact between the semiconductor quantum dots and graphene. The specific method involves: (1) preparing molybdenum disulfide quantum dots using one-step chemical synthesis by (1a) dissolving 0.20-0.50 g sodium molybdate dihydrate in 30 ml deionized water and ultrasonically dispersing for 30 minutes to obtain a solution (A), (1b) dissolving 0.08-0.14 g thiourea in 30 ml ethanol and then subjecting to ultrasonic dispersion treatment for 30 minutes to obtain a solution (B), (1c) evenly mixing the solution (A) and solution (B), then putting into a reaction kettle, and heating at 180-220 degrees C for 12-18 hours to obtain a suspension and (1d) collecting the suspension in step (3), dispersing in an ice bath, ultrasonically processing for 1 hour, centrifuging at 10000 rpm for 10 minutes, and collecting the supernatant to obtain a molybdenum disulfide quantum dot solution dispersed in an aqueous ethanol solution; (2) carrying out spin-coated uniform modification on semiconductor quantum dots on graphene prepared by chemical vapor deposition by spin coating the above quantum dot solution by chemical vapor deposition on the graphene sample, where the speed of the spin coater is 600-1000 rpm, to obtain a molybdenum disulfide quantum dot/graphene hybrid film; and (3) preparing the gas sensor by (3a) putting the molybdenum disulfide quantum dot/graphene hybrid film obtained in step (2) into an oven and annealing at 80-120 degrees C for 0.5-2 hours under vacuum and (3b) coating a conductive silver paste as an electrode on the molybdenum disulfide/graphene sample obtained after annealing, constructing a device to fabricate the sensor.